<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title></title>
    <style>
        table {
            text-align: center;
            line-height: 14px;
            border-collapse: collapse;
        }

        .tb1 {
            width: 800px;
            position: relative;
        }

        .tb2 {
            width: 100%;
        }
    </style>
</head>
<body>
<table class="tb1" border="1">

    <tr>
        <td>asdad</td>
    </tr>
    <table border="1" class="tb2">
        <tr>
            <td>哈哈1</td>
        </tr>
        <tr>
            <td>哈哈2</td>
        </tr>
    </table>


</table>


</body>
</html>